Abstract

The current classification system for the Monocelididae which is based on the character "presence or absence of an accessory prostatoid organ" divides the family into two subfamilies, namely the Minoninae and the Monocelidinae. However, other characters relating to the structure of the male copulatory bulb and to karyotypes do not support this division. Monocelidid male copulatory bulbs can be either of the simplex or the duplex-type, and if this character is mapped onto the current classification, then both subfamilies contain species with either type of copulatory bulb. We therefore decided to construct an independent phylogeny for the Monocelididae using nucleotide-sequence data of the gene coding for the 26/28S rDNA. Distance- and parsimony-based analyses resulted in phylogenetic trees that strongly supported a division of the Monocelididae based on characters of the male copulatory bulb and not on the accessory prostatoid organ. Thus, all species possessing a simplex-type copulatory bulb cluster together into one monophyletic group, the Monocelidinae (sensu Midelburg), whereas species characterized by a duplex-type copulatory bulb constitute a paraphyletic assemblage.